燕山期构造热事件对太原西山煤层气高产富集影响

INFLUENCE OF THE TECTONIC THERMAL EVENTS IN YANSHAN EPOCH ON COALBED METHANE ENRICHMENT AND HIGH-PRODUCTIVITY IN XISHAN COAL FIELD IN TAIYUAN

太原西山煤田是位于沁水盆地西北侧的一个石炭—二叠系煤田,在燕山期发生的岩浆侵入事件在该 煤田形成了异常的古地热场,使煤级在短暂地质时限内迅速增高。该煤田煤层经历了两次生气过程,在第二次生 烃过程中完成了主要生气历程,构造热事件大大提高了煤层生气量,从而给煤层气的富集创造了有利气源条件;同 时中生代地热场具有大地热流量高和瞬时性的特点,形成了大量岩浆诱发成因的煤层割理,提高了煤层的渗透率, 使该地区煤层气资源具有很大的勘探潜力。

Xishan coal field in Taiyuan is located in northwest Qinshui basin and composed of Carboniferous-Permian coal beds. An abnormal paleogeothermal field was formed owing to the occurence of magma intrusion in Yanshan epoch, which caused the coal rank in the field to be rapidly increased in a short geological time limit. The coal beds in the field had experienced two hydrocarbon-generation stages and the main gas-generation course finished during the second stage. The tectonic thermal events had greatly raised the gas generating amount in the coal beds, thus creating a beneficial gas-source condition for coalbed methane enrichment. Meanwhile, the Mesozoic geothermal field was characterized by large terrestrial heat flow, rate and its in stantaneity, and a great number of magma-caused coal cleats were formed, thus enhancing coal reservoir permeability. Therefore, the coalbed methane resources in this region are of great exploration potential.